1. Field of the Invention
The invention relates to a heat-dissipating mechanism for a projecting device, more particularly to a heat-dissipating mechanism for a thin-type projecting device.
2. Description of the Related Art
Referring to FIG. 1, a conventional projector 1 includes a casing 11, and an optical engine 12, a blower 13, two axial fans 14, a power supply 15, and a control circuit board (not shown) disposed in the casing 11. The casing 11 includes a lower casing body 111 and an upper casing body (not shown) covering the lower casing body 111. The optical engine 12 includes a light source module 121 disposed in the lower casing body 111, and an imaging module 122. The light source module 121 includes a lampshade 123 and a burner (not shown) disposed in the lampshade 123. The light source module 121 generates lighting power of 200 W. The control circuit board is disposed on a bottom face of the upper casing body, and is connected electrically to the imaging module 122 for controlling images projected by the imaging module 122. The blower 13 is disposed at a front left side of an open end 124 of the lampshade 123 for driving air currents to cool the burner within the lampshade 123. Therefore, the blower 13 is generally referred to as a lamp blower of the projector 1. The two axial fans 14 are disposed in the lower casing body 111, and are located at one side of the lampshade 123 for driving air currents to cool the lampshade 123 and other optical components within the casing 11. Therefore, the axial fans 14 are generally referred to as system fans of the projector 1. The power supply 15 is disposed in the lower casing body 111, and is located at a front side of the two axial fans 14 for providing part of working voltage for the burner within the lampshade 123 of the light source module 121.
Referring to FIG. 1 and FIG. 3, FIG. 3 shows the characteristics of the system fans used by the projector 1 and the amount of airflow in the system calculated from numerical simulation. The length (L) width (W), and thickness (T) of each of the axial fans 14 of the projector 1 are 45 mm×45 mm×15 mm. The maximum amount of airflow calculated in the absence of air impedance is 10.3 CFM. However, the maximum static pressure that the axial fan 14 can provide is 0.1 in H20. That is, the capability of the axial fan 14 to resist air impedance is limited, and the axial fan 14 is incapable of effectively overcoming the high air impedance characteristic associated with a thin-type projector system. Consequently, after the maximum amount of airflow of 20.6 CFM that the two axial fans 14 provide is subjected to the air impedance within the system, the amount of airflow actually provided by the two axial fans 14 is merely 5.9 CFM, which, when combined with the amount of airflow provided by the blower 13, gives the amount of airflow of 8.1 CFM for the total system. This apparently cannot meet the requirements of the projector 1 which requires the amount of airflow of 10 CFM, thereby resulting in increased temperature during operation of the burner of the light source module 121. Therefore, when the air inside the system is discharged through an air outlet 113 in a rear side wall 112 of the lower casing body 111, the temperature at the air outlet 113 is also increased, thereby generating safety concerns and reducing system reliability.
Referring to FIG. 2, another conventional projector 2 is shown to have substantially the same structure as that of the conventional projector 1 shown in FIG. 1. The difference merely resides in that two axial fans 24 of the projector 2 are disposed on a rear side wall 212 of a lower casing body 211 immediately next to an air outlet 213. By varying the mounting positions of the two axial fans 24, the amount of airflow actually provided by the two axial fans 24 combined with the amount of airflow of a blower 23 reaches 12.8 CFM (as shown in FIG. 3). However, the amount of airflow actually provided by the two axial fans 24 is merely 9.7 CFM (as shown in FIG. 3), which is less than 50% of the maximum amount of airflow thereof. Therefore, the actual output efficiency is evidently unsatisfactory. In addition, since the two axial fans 24 draw in the hot air generated in the interior of the system via air inlets 241 of the axial fans 24 and discharge the same through the air outlet 213 in the rear side wall 212, the temperature around the air inlets 241 of the two axial fans 24 exceeds the highest working temperature (70° C.) of fans generally manufactured in the fan industry, and accordingly has a significant impact on the service life and reliability of the two axial fans 24.
On the other hand, a blower with a smaller thickness and larger length and width is currently used as a system fan in projectors in the industry. The blower is disposed in a casing of the projector in a horizontal fashion. However, in order to effectively provide the system with a sufficient amount of airflow, except for the thickness of the blower which is required to match the thickness of the casing and is therefore unalterable, the length and width of the blower need to be sufficiently large, so that the static pressure value of the blower is increased to provide airflow required by the system. Such an arrangement inevitably results in an increase in length and width of the casing of the projector, so that the projector occupies a relatively larger amount of space in use, and renders carrying of the projector inconvenient.